The present invention relates to suspensions for relatively heavy vehicles such as mining trucks, and more particularly the present invention relates to a suspension for a rigid axle assembly that permits the axle assembly to pivot or oscillate about an axis that projects longitudinally of the vehicle.
Typically, an articulated mining truck has four wheels that are provided with four wheel drive, and its front axle is suspended so that it can oscillate through plus or minus 6.degree. about the longitudinal axis of the vehicle. Such pivoting capability is desireable because otherwise traction may be lost in the event one of the driven front wheels leaves contact with the ground. Loss of traction must be avoided because the steering of the truck, of course, depends upon good traction of both front wheels.
In one prior art example of a pivotal suspension for the front axle of an articulated mining truck, the front wheels are mounted to a rigid axle assembly that is, in turn, mounted upon a bolster plate structure. The bolster plate is pivotally mounted to the chassis of the front section of the truck by a pair of journal bearings that permit the bolster plate to pivot about a longitudinal axis through the bearings, thereby permitting the front axle assembly to oscillate sideways relative to the chassis. This bolster plate type of suspension requires accurate alignment of the bearings with respect to each other and the longitudinal axis of the vehicle.
In some other prior art mining trucks, the rigid front axle assembly is directly supported upon a pair of leaf springs located near the wheels. This type of suspension permits the axle assembly to oscillate sideways and also to move vertically under shock loading. That is, the leaf springs not only permit the axle assembly to tilt, but they also absorb shocks, thus smoothening the ride and reducing driver fatigue.